Cyanide Metabolism in Relation to Ethylene Production in Plant Tissues

Abstract

HCN is the putative product of C-1 and amino moieties of 1-aminocyclopropane-l-carboxylic acid (ACC) during its conversion to ethylene.In apple (Malus sylvestrus Mill.) slices or auxin-treated mungbean (Vigna radiata L.) hypocotyls, which produced ethylene at high rates, the steady state concentration of HCN was found to be no higher than 0.2 micromolar, which was too low to inhibit respiration (reported Ki for HCN to inhibit respiration was 10-20 micromolar). However, these tissues became cyanogenic when treated with ACC, the precursor of ethylene, and with 2-aminoxyacetic acid, which inhibits 6-cyanoalanine synthase, the main enzyme to detoxify HCN; the HCN levels in these tissues went up to 1.7 and 8.1 micromolar, respectively. Although ethylene production by avocado (Persea gratissima) and apple fruits increased several hundred-fold during ripening, f-cyanoalanine synthase activity increased only one-to two-fold. These findings support the notion that HCN is a co-product of ethylene biosynthesis and that the plant tissues possess ample capacity to detoxify HCN formed during ethylene biosynthesis so that the concentration of HCN in plant tissues is kept at a low level.Plant hormone ethylene is produced by all plants and in trace amounts elicits many physiological responses. Ethylene is biosynthesized in plants via the following sequence: methionine -* S-adenosylmethionine --+1 -aminocyclopropane-1 -carboxylic acid --C2H4 (19). In the biological oxidation of ACC2 to ethylene, it has been shown that carboxyl carbon, C-1, and C-2,3 of ACC are metabolized into C02, ,3-cyanoalanine derivatives, and ethylene, respectively (11,12). Although no free HCN was identified, it was asserted that C-1 of ACC is initially liberated as HCN but is rapidly conjugated into ,B-cyanoalanine derivatives as soon as it is liberated. This notion was based on the observation that the metabolic fate of the C-1 of ACC during its conversion to ethylene was identical to that of administered HCN and that the amount of HCN-conjugates formed was equivalent to that of ethylene produced (1 1 (3-cyanoalanine) ,-Cyanoalanine synthase is widely distributed in higher plants (9). ,3-Cyanoalanine thus formed is further metabolized to asparagine or to y-glutamyl-,3-cyanoalanine (1-4, 6, 9, 11, 12 MATERIALS AND METHODS Plant Materials. Apple (Malus sylvestrus Mill., var Golden Delicious) slices (1 cm in diameter, 0.5 cm in length) were prepared from fruits harvested from a local orchard and stored at 0°C. Avocado (Persea gratissima) were purchased from the local market. Mungbean ( Vigna radiata L.) hypocotyl segments (2 cm long) were prepared from 3-d-old etiolated seedlings grown at 25°C.Incubation Conditions. Apple slices were presoaked in 2% KCI solution containing specified chemicals in a 50-mL flask for 2 h, blotted dry, and then incubated at 25°C in a 10-mL flask sealed with a serum cap. Each flask contained a plastic center well with 200 gL of 0.1 N NaOH to trap the released HCN. Mungbean hypocotyls were similarly treated as apple slices ...

Effect of 2,4-Dichlorophenoxyacetic Acid on Endogenous Cyanide, β-Cyanoalanine Synthase Activity, and Ethylene Evolution in Seedlings of Soybean and Barley

“…A similar response was not observed in identically treated barley plants. Similar increases in endogenous cyanide have been reported for apple slices and mungbean hypocotyls treated with ACC or a combination of ACC and aminooxyacetic acid (30). Those results support our findings regarding the effect of exogenously supplied auxin on endogenous levels of cyanide since one of the effects of applied auxin is to increase the amount of endogenous ACC (29).…”

“…In fact, data from isotope dilution experiments between this study and that of Yip and Yang (30) (30). The most probable explanation is that significant amounts of cyanide were artifactually derived from noncyanogenic compounds during bromination of tissue extracts.…”

“…Similar results were achieved when effluent air from a gassing flask was passed through an NaOH trap and an aliquot of the trapping solution was analyzed colorimetrically. Given the greater solubility of HCN as opposed to ethylene, and the fact that intact plants, not tissue slices (30), were used, the possibility existed that endogenously produced cyanide was either not released or released in amounts too low to detect. In either case, cyanide should be detectable in tissue extracts.…”

Mango (Mangifera indica L.) malformation: a malady of stress ethylene origin

“…Cyanogenic compounds are present in plants in form of stable compounds like cyanogenic glycosides. In case of tissue disruption and infection hydrogen cyanide is released from cyanogenic compounds, (Yip and Yang 1988;Ansari et al 2013a). Over production of stress ethylene causes fused lobed anther with weakened pollen grains and curved stigma with poor stigmatic face, which limits successful fertilization and thereby no fruit set (Rani et al 2013).…”

Role of ethylene in abnormal shoot growth induced by high concentration of brassinolide in rice seedlings

“…8) In plant tissue, cyanide is produced as a co-metabolite during the enzymatic conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. 9) In this study, we analyzed the action mechanism of BL that induces abnormal shoot growth under light. Because BL can have opposite effects on plant growth at the same concentration, we assumed that ethylene was involved in its action mechanism.…”